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1. Field of the Invention
The invention relates to the field of fiber optic systems, and in particular, to an amplification system that amplifies a C-band and L-band of an optical signal using a laser signal.
2. Description of the Prior Art
Fiber optic systems transfer data over optical fibers. Designers of fiber optic systems try to increase the capacity of the system to accommodate more data traffic and the Internet. Wavelength Division Multiplexing (WDM) increases the capacities of the fiber optic system. WDM passes multiple data channels over one or more wavelengths of light simultaneously over a single fiber. To further increase the fiber optic system capacities, high-speed data transfers are used. The high-speed data transfers require high-power optical signals.
Currently, amplifiers supply the optical signals with sufficient power for the high-speed data transfers. The amplifiers include boost amplifiers, line amplifiers, and pre-amplifiers. A problem with the current fiber optic systems is that as the amplifiers increase the power of the optical signals, impairments affecting the optical signals increase due to non-linearities in the fiber. The impairments cause errors in the fiber optic system and increase a Signal to Noise Ratio (SNR) and an overall Bit Error Rate (BER) of the system.
One solution to the above problem is a distributed optical amplification system that uses remote pump technology. A remotely pumping laser coupled to a conventional transmission fiber can amplify certain wavelengths of optical signals traveling over the fiber. The pump laser replaces some conventional amplifiers in the system and decreases the required output power level of the remaining amplifiers. The laser signal at a wavelength of 1480 nm amplifies signals traveling in a range of wavelengths of approximately 1565 nm-1600 nm. The range of wavelengths of 1565 nm-1600 nm is referred to as the L-band. The laser signal amplifies the L-band due to a Raman effect. The Raman effect causes an increase in a gain of a wavelength of light traveling over a transmission fiber when a light wave, such as the laser signal, of a lower wavelength is concurrently transmitted over the fiber. The Raman effect is well known in the art. Unfortunately, the pump laser only amplifies the L-band and does not amplify signals in the other wavelengths.
A second laser signal at a wavelength of 1400 nm amplifies signals traveling in a range of wavelengths of approximately 1525 nm-1560 nm. The range of wavelengths of 1525 nm-1560 nm is referred to as the C-band. The laser signal amplifies the C-band due to the Raman effect. Unfortunately, the amplification system requires two high-powered pump lasers to amplify the C-band and L-band. The high-powered lasers increase the overall cost of the fiber optic system.
An amplification system that amplifies a C-band and L-band in an optical signal using a single laser signal solves the above problems. The amplification system is comprised of a signal processing system and a laser system. The laser system receives the laser signal and transfers the laser signal to the signal processing system. The signal processing system receives the optical signal that includes the C-band and L-band and the laser signal, and combines the optical signal and the laser signal to amplify the C-band and L-band of the optical signal. The amplification system transfers the optical signal that includes an amplified C-band and L-band. Advantageously, the amplification system amplifies the C-band and L-band with the single laser signal instead of two laser signals.
In one embodiment of the amplification system, the signal processing system is comprised of a splitter coupled to a coupler by a first fiber and a second fiber. The first fiber is an Erbium-doped fiber. The second fiber is a conventional transmission fiber. The laser system is comprised of a pump laser coupled to the coupler. The splitter splits an optical signal that includes the C-band and L-band and transfers the optical signal over the first fiber and the second fiber. The pump laser generates a single laser signal and transfers the laser signal through the coupler and over the first fiber and the second fiber in an opposite direction of the optical signal. In the first fiber, the optical signal and the laser signal combine to amplify the C-band of the optical signal based on the Erbium properties of the first fiber. In the second fiber, the optical signal and the laser signal combine to amplify the L-band of the optical signal based on a Raman effect. The amplification system in this embodiment is an advance because it amplifies both the C-band and L-band of the optical signal using the laser signal. The amplification system reduces the need for conventional amplifiers and reduces the output power needs of remaining amplifiers.
In another embodiment of the amplification system, the signal processing system is comprised of a section of Erbium and Phosphorus doped fiber and a section of conventional transmission fiber. The laser system is comprised of a pump laser coupled to the signal processing system. The pump laser transmits a single laser signal over the Erbium and Phosphorus doped fiber and the transmission fiber in an opposite direction of an optical signal that includes the L-band. In the section of Erbium and Phosphorus doped fiber, the optical signal and the laser signal combine to amplify the L-band of the optical signal based on the properties of the section of Erbium and Phosphorus doped fiber. In the transmission fiber, the optical signal and the laser signal combine to amplify the L-band of the optical signal based on the Raman effect. The amplification system in this embodiment produces a flatter gain shape for the L-band and eliminates the need for a gain equalization filter.